Effects of sodium chloride on adsorption at different interfaces and aggregation behaviors of disulfonate gemini surfactants

Abstract

Effects of NaCl on adsorption of dialkylated diphenyl ether disulfonate gemini surfactants (C_n-DADS, n = 8, 10 and 12) at different interfaces were studied by equilibrium surface tension, dynamic surface tension, interfacial tension and wetting measurements. The results show that the critical micelle concentration (cmc) values of C_n-DADS aqueous solutions decrease with an increase in NaCl concentration. For C₈-DADS aqueous solution, the values of the surface tension at cmc (γ_cmc) keep almost invariable with the addition of NaCl. The monomer diffusion coefficient (D_eff) values of C_n-DADS increase with an increase in both alkyl chain length and inorganic salt concentration. The interfacial tensions (IFTs) between C_n-DADS solutions with various amount of NaCl added and dodecane slightly decrease with the increase of NaCl concentration. The equilibrium contact angle values decrease significantly firstly and then no further change with increasing the NaCl concentration. The vesicles are formed in both 0.5 mM C₈-DADS aqueous solution and 2 mM C₈-DADS solution with 0.1 M NaCl.